This invention relates generally to an apparatus or device and process for cleaning in an electrostatographic printer, and more particularly, a cleaning blade lubricant used therein to prevent the build up of frictional forces between the cleaning blade and the photosensitive surface.
In the process of electrophotographic printing, a photoconductive surface is charged to a substantially uniform potential. The photoconductive surface is imagewise exposed to record an electrostatic latent image corresponding to the informational areas of an original document being reproduced. This records an electrostatic latent image on the photoconductive surface corresponding to the informational areas contained within the original document. Thereafter, a developer material is transported into contact with the electrostatic latent image. Toner particles are attracted from the carrier granules of the developer material onto the latent image. The resultant toner powder image is then transferred from the photoconductive surface to a sheet of support material and permanently affixed thereto.
This process is well known and useful for light lens copying from an original and printing applications from electronically generated or stored originals, and in ionography.
Various methods and apparatus may be used for removing residual particles from the photoconductive imaging surface. Hereinbefore, a cleaning brush, a cleaning web, and a cleaning blade have been used. Both cleaning brushes and cleaning webs operate by wiping the surface so as to affect transfer of the residual particles from the imaging surface thereon. After prolonged usage, however, both of these types of cleaning devices become contaminated with toner and must be replaced. This requires discarding the dirty cleaning devices. In high-speed machines this practice has proven not only to be wasteful but also expensive.
The shortcomings of the brush and web made way for another now prevalent form of cleaning known and disclosed in the art--blade cleaning. Blade cleaning involves a blade, normally made of a rubberlike material (e.g. polyurethane) which is dragged or wiped across the imaging surface to remove the residual particles from the imaging surface. Blade cleaning is a highly desirable method, compared to other methods, for removing residual particles due to its simple, inexpensive structure.
However, there are certain deficiencies in blade cleaning, which are primarily a result of the frictional sealing contact that must occur between the blade and the surface. One such deficiency is often experienced prior to initial start-up of the electrophotographic printing machine cleaning process. At start-up, the cleaning apparatus in the electrostatographic printing machine, has no initial lubrication between the cleaning blade edge and the photosensitive imaging surface. This lack of lubrication allows the build-up of frictional forces between the cleaning blade edge and the imaging surface. Dynamic friction is the force that resists relative motion between two bodies that come into contact with each other while having separate motion. This type of frictional problem occurs in both cartridge assemblies used in customer replacement units (i.e. CRUs) and permanently attached printer cleaning systems. The friction between the blade edge and the imaging surface becomes so great at start-up that it causes the cleaning blade to "foldover" (i.e. the blade edge flips over onto itself). Foldover causes the blade material to experience high stress thereby damaging the cleaning blade. Foldover also affects the ability of the cleaning blade edge to form a proper sealing contact with the imaging surface for cleaning. As a result of foldover affects such as these, the cleaning blades often fail prior to their first use which leads to frequent blade replacement. It is an object of the present invention to reduce the build up of the frictional forces at start-up in order to reduce the amount of cleaning blade replacement required due to damaged and failed cleaning blades. It is believed that the present invention aids in correcting misalignment between the blade and the photoreceptor surface created by the photoreceptor roller's misalignment providing a better sealing contact.
Various blade lubricating materials have been attempted to provide sufficient adherence to the blade surface. However, it has been found difficult to keep the lubricant adhered to the cleaning blade, especially when the lubricant is applied prior to shipping and packaging. Solid lubricants (e.g. Kynar) tend to fall off the cleaning blade and liquid lubricants, when dry, tend to become brittle and flake off the cleaning blade edge prior to installation in the electrostatographic printing machine. The portion of lubricant remaining at the time of installation of the blade is often not effective to reduce the build-up of friction when the cleaning blade and the imaging surface make initial contact at start-up. Some reasons for this ineffectiveness are that the lubricant remaining is not enough to reduce the friction, or there is no lubricant remaining on the cleaning edge when it contacts the imaging surface. It is an objective of the present invention for the lubricant slurry to remain adhered to the cleaning blade edge after drying and operate effectively upon installation.
It is also an object of this invention to decrease the likelihood of blade damage and failure upon initial start-up conditions.
It is a further objective of the invention to prevent the introduction of any new ingredients not already present in the process, thereby eliminating the possibility of unexpected subsystem interactions such as photoreceptor filming, cometing, and the like.
The following disclosures may be relevant to various aspects of the present invention and may be briefly summarized as follows:
U.S. Pat. No. 3,552,850 to Royka et al. discloses an imaging system which employs a reusable electrostatographic imaging surface cleaning station comprising at least one self-adjusting flexible cleaning blade for pressure contact cleaning of the imaging surface and a means to supply a dry solid lubricant to the imaging surface. The patent states that a dry solid lubricant may be supplied to an interface between the cleaning blade and the imaging surface by, for example, having the lubricant in a solid form and having it intimately mixed with toner which is supplied to the imaging surface during development of the electrostatic image.
U.S. Pat. No. 4,519,698 to Kohyama et al. discloses an image forming apparatus which includes a cleaning blade and a drum lubricant. The patent states that a recess is formed at part of an outer circumferential surface that holds lubricant and the tip end of the cleaning blade feeds the lubricant in the recess to part of the outer circumferential surface of the photosensitive drum which is brought into contact with the cleaning blade to form a thin film of lubricant by rotation of the drum. The lubricant is mixed with the developer and its thickness is kept uniform upon the photoresponsive drum.
U.S. Pat. No. 4,883,736 to Hoffend et al. discloses a toner composition of resin particles, pigment particles and a wax component comprised of polymeric alcohols.
U.S. Pat. No. 4,958,197 to Kinashi et al. discloses a cleaning blade for an image forming apparatus which is formed of a rubber elastomer which contains, or has adhered on the surface thereof, an antistatic agent in an amount effective to prevent electrification. The patent states that by virtue of the antistatic agent on the cleaning blade, scattering of toner particles adhering to the blade edge surface is realized within a very short time. The toner particles serve as a lubricant to prevent the blade from excessive stress due to friction.
U.S. Pat. No. 4,970,560 to Lindblad et al. discloses a lubricated metal cleaning blade for use in dry electrophotographic processes wherein a hardened material coating is electro-deposited onto a carbon steel cleaning blade. The patent states that the coating process is selected to provide a microporous surface which is sealed with sub-micron size particles of flourocarbons, heat treated to create a smooth, slippery surface, while the hardened metal coating provides wear resistance to friction encountered during the cleaning operation. In addition, it is disclosed that the process gives the blade improved hardness, protection against chemical attack, better abrasion resistance, permanent lubricity (until the blade edge is undesirably worn), provides a marked increase in life, and appears to improve the squareness of edges on the blades.
U.S. Pat. No. 4,971,882 to Jugle discloses a toner composition comprised of resin particles, pigment particles, a charge enhancing additive, and a mixture of a charge enhancing additive and a wax component comprised of an alkylene or polymeric alcohol. The patent states that the toner and developer compositions contain a wax mixture wherein the wax includes polyethylene, polypropylene and linear polymeric alcohol available as Unilin.RTM. comprised of a fully saturated hydrocarbon backbone with at least 80 percent of the polymeric chains terminated at one chain end with a hydroxyl group. The patent discloses that the toner and developer composition enables images of excellent quality inclusive of acceptable resolutions with no toner spots on the photoreceptor.